pisidiidæ

Century Dictionary and Cyclopedia

1. A family of dimyarian bivalves, typified by the genus Pisidium. They have the branchial and pedal orifices confluent, the anal siphonate, the foot large, the shell equivalve and oval or cuneiform, with the area in front of the umbones larger than that behind, the hinge with two divergent cardinal teeth in each valve and four lateral teeth in the right and two in the left valve, and an external ligament. These small bivalves inhabit fresh water, and are remarkable for the posterior position of the umbones.